Certain Americans' heads are getting larger at a "dramatic" rate, say researchers at the Forensic Anthropology Center at the University of Tennesse, citing a 6.8 per cent increase in skull length in the past 100 years across their sample.
At this rate, the heads of this group of Americans will have doubled in length sometime …

Or conversely,

Re: Make sense

>Americans are known for their superior intellect.

Brought to by Carl Jr's Big Ass Fries tm. Idiocracy makes a lot more sense than this garbage. Still thank goodness for IQ being one of those traits that push towards the mean regardless of parents genetics (ie two stupid people or two smart people children tend to move towards the average) or else we would be putting Brawdo on our crops.

Of many explanations

Re: Of many explanations

Very true, but perhaps unnecessary.

A height increase of 5.6% is mentioned over the same period. (The article says this has stopped in recent years, but there's no evidence that the head increases haven't stopped, too.) That's a volumetric increase of 17%, which on an average modern brain size of 1260 cm3 (wikipedia) would be an increase of 190cm3 from an inferred 19th century value of 1070cm3.

Re: Their is an easy remedy...

Unlikely to be evolution

Isn't this more likely to be due to improved diet than evolution?

Up until the last century, greater intelligence would have given an evolutionary advantage; and this may still be the case in undeveloped countries. But I would argue that in the developed West, including America, intelligence is no longer a trait that leads to successful breeding.

Re: Unlikely to be evolution

The evolutionary advantage of higher intellect seems to be very flimsy, and 100 years is just 5 generations or so. There's no way evolution has any measurable effect on something so poorly correlated to reproduction in just 5 generations. It's probably due to diet or medicines or something like that.

Relaxed evolution...

Re: Relaxed evolution...

Not in 5 generations, and not for something this subtle. Evolution can be fast, but only when there's spectacular selective pressure (like, a deadly virus or a genocide).

That said, I like the infant mortality explanation. Big-headed babies are less likely to die at birth today. I just think that the observed increase is almost entirely explainable as a statistical effect, not an evolutionary one. I.e. the same number of big-headed babies are conceived as a century ago, but more of them survive birth today. This can cause an evolutionary effect so that more big-headed babies are actually conceived, but it would take hundreds of generations.

Evolution at its finest

Environmental, Not Evolutionary

Something has affected head size the same way diet affected height. Humans haven't evolved to be any taller since we were cavemen. In fact palaeolithic humans on a largely fatty, meat based diet were quite tall, with heights comparable to today. It was during the switch to a neolithic diet largely composed of grains and vegetables with sparing amounts of meat and dairy that caused height to take a nosedive until the 20th century. Since we now can all afford to eat whatever we want, with ample amounts of marconutrients even in the worst junk food diet, that height has probably stopped increasing generation by generation. The same will no doubt happen for head size.

It's all those 32oz sodas

"They found that in that time skull capacity had increased by 200 cubic centimetres for men in the sample, equivalent "to the size of a tennis ball". The researchers found that the average height from the base to the top of the skull in men had increased by 8mm. In the women in the sample, the corresponding increases were 7mm and 180 cubic centimetres."

If I read this correctly, in women the skull capacity increased by 7mm while the body has increased by 180 cubic centimetres. That accounts for all the fat American ladies.

More likely...

Very Good News

Well, if the human brain were getting larger, that would be very good news.

It doesn't even have to complicate childbirth. If our brains just kept on growing at the same rate, rather than slowing down their rate of growth when we are two years old, we could have our heads stay the same size at birth, and yet have much larger brains as adults.

Size doesn't matter, it's what you do with it

Re: Very Good News

Oh it comes down to this silly practice. Once a women has one c-section, all of her kids after that will be delivered by c-section. They don't even check to see if it's necessary. It comes down to well thats they way we have always done it .